Jody Victor: The health of the Great Lakes ecosystems has improved remarkably since the 1970s. The presence of organic contaminants, however, persists at low levels and continually circulates within the aquatic food web. The effects of long-term exposure to these chemicals may remain detrimental to the health of Great Lakes eagles.
Food is the primary vehicle that moves contaminants, including heavy metals, into eagles’ bodies. In the 1970s mercury and lead were considered contributors to the decline of Bald Eagle populations. However, research at that time failed to demonstrate a cause and effect relationship between exposure to heavy metals and population decline.
Mercury is a naturally occurring element that is virtually ubiquitous in the environment. Also, it is released into the atmosphere through naturally occurring and manufacturing processes. Human-made sources of mercury include mining and smelting, pulp and paper production, burning of fossil fuels and wood, petroleum refining, and solid-waste incineration. An estimated two-thirds of the mercury in the atmosphere originates from these sources.
Ultimately, mercury in the atmosphere deposits on the earth and makes its way into aquatic systems, the discovery of mercury-contaminated fish in relatively undisturbed Canadian lakes was one of the first clues that acid rain may be an indirect conduit of mercury. Consumption of fish that is contaminated with mercury is known to be hazardous to wildlife and human health. Toxic at very low concentrations, mercury can accumulate in the body’s tissues. It will impair neurological function and complex behavior.
Determining whether mercury exposure is a long-term problem that is responsible for reducing longevity, and hence breeding potential, of Bald Eagles in the Great Lakes, is one of the next questions that the Bald Eagle recovery team would like to explore. Anything that reduces adult longevity and long-term productivity to a notable degree has the potential to result in population decline – even if short-term population growth appears to be sufficient to sustain the species.